Organic light emitting diode displays are self-luminous display devices that use organic light emitting diodes to emit light to display images. Unlike liquid crystal displays, organic light emitting diode displays do not require separate light sources, and thus, thickness and weight can be reduced. Moreover, organic light emitting diode displays exhibit high quality characteristics such as low power consumption, high luminance, fast response speeds, and the like, and thus are being highlighted as next generation display devices for portable electronic devices.
Various attempts are being made to reduce power consumption and improve efficiency of organic light emitting diode displays. For instance, a material having high charge mobility is used for a hole injection layer, a hole transporting layer, and the like, in order to achieve low voltage, high efficiency, and a long service life.
FIG. 1 schematically illustrates a structure of an organic light emitting diode display capable of being driven at low voltage.
Referring to FIG. 1, the organic light emitting diode display includes first, second and third pixel electrodes as a first electrode 20 on a substrate 10. The first electrode 20 is divided into pixel units by a pixel defining layer (PDL) 30. On the first electrode 20 and the pixel defining layer 30, an interface p-doped layer 41, a hole transporting layer 42, an intermediate p-doped layer 43, and a light emitting layer 50 are formed. In this case, the light emitting layer 50 is divided into a red light emitting layer, a green light emitting layer, and a blue light emitting layer. On the light emitting layer 50, a common electrode is formed as a second electrode 60. A hole injection layer may be additionally disposed between the first electrode 20 and the hole transporting layer 42, or only the hole injection layer (instead of the hole transporting layer 42) may be disposed. In addition, at least one of an electron injection layer and an electron transporting layer may be disposed between the light emitting layer 50 and the second electrode 60.
FIG. 2 schematically illustrates another example of an organic light emitting diode display having a structure including a substrate 10, a first electrode 20, organic layers 41, 42, and 43, a light emitting layer 50, and a second electrode 60. Here, as the organic layers, an interface p-doped layer 41, a hole transporting layer 42, and an intermediate p-doped layer 43 may be disposed. In order to improve the interface characteristic between the materials of the first electrode 20 and the hole transporting layer 42, the interface p-doped layer 41 (partially doped with a p-dopant) is applied to a boundary between the layers. In this case, in order to improve service life and driving voltage, a p-dopant doped region (i.e., the intermediate p-doped layer 43) is additionally disposed on the hole transporting layer 42 as well as the boundary with the first electrode 20. The intermediate p-doped layer 43 is formed as a common layer of a first pixel electrode, a second pixel electrode, and a third pixel electrode together with the interface p-doped layer 41.
However, in the organic light emitting diode display as described above, the intermediate p-doped layer 43 is formed using a material having high charge mobility, and when formed as a common layer, the p-doped layer may become a path for the movement of electric charges (holes). As a result, the p-doped layer 43 may serve as a lateral leakage path through which electric charges can flow into another adjacent pixel while driving any one pixel. In addition, when driving a single color due to lateral leakage current, an adjacent pixel of a different color is also driven, and thus it is difficult to implement the proper color. Further, grays are not smoothly displayed at low luminance, which may lead to color-mixing.